Journal of Morphology最新文献

Over the course of its evolution, the human soleus muscle has rapidly increased in size and gained a more important role in bipedal locomotion. However, the detailed processes underlying these morphological changes remain uninvestigated. When discussing these morphological changes in muscles, the innervation patterns among primates is an important criterion to consider and compare. In this study, we comprehensively investigated the detailed intramuscular nerve distribution patterns of the soleus muscle in nine extant primate species and provide new evolutionary implications. The human soleus muscle is innervated by two branches of the tibial nerve: the posterior nerve branch innervates the major posterior part of the soleus muscle, and the anterior nerve branch innervates the anterior bipennate part of the soleus muscle. The soleus muscle is innervated by the posterior branch in all species and by the anterior branch in five of the nine primate species. The prevalence and distribution patterns of the anterior branches varies even between closely related species. However, these variations were not associated with the intramuscular distribution patterns of the posterior branches. Therefore, the distribution of the anterior and posterior branches may have evolved independent of each other. In humans, the anterior branch and intramuscular subbranch of the posterior branch—that innervates the muscle fascicles originating from the soleal line on the tibia—are distributed more widely within the soleus muscle than in non-human primates. This rapid increase in size and medial expansion of the soleus muscle over the course of human evolution may be due to the expansion of the two parts of the soleus muscle innervated by these two branches.

Scanning electron microscopy (SEM) is a fundamental technique to study the morphology of anuran embryos and tadpoles. Here, we present a drying method for SEM imaging of late frog embryos using commonly available dehydration solvents such as ethanol or methanol, xylene, and applying low temperature vacuum freeze drying. Briefly, embryos from early embryonic gills development to hatching were fixed with a paraformaldehyde—glutaraldehyde mix, then dehydrated to ethanol or methanol, and then slowly dried using low temperature and constant vacuum pressure. An extra step of clearing using xylene after ethanol dehydration improved results considerably. Our protocol successfully preserved embryo shape and the morphology of fragile and delicate superficial structures (e.g., external embryonic gills, apical ectodermal microridges and surface ciliation), while avoiding the use of some SEM toxic reagents.

The Anji Salamander (Hynobius amjiensis) is a critically-endangered amphibian endemic to the Tianmushan Mountain area in southeastern China. As most of its congeneric species in the ancestral salamander family Hynobiidae, the osteology of H. amjiensis has remained essentially unknown and has hampered efforts in understanding morphological evolutionary patterns of early salamanders. Here, we investigate the skeletal anatomy of H. amjiensis based on microcomputed tomography scans of post-metamorphosed juvenile and adult specimens. Our results reveal Hynobiidae has more early-tetrapod-like plesiomorphic characters than expected, as H. amjiensis has a stapedial foramen in the middle ear and two centralia and a centrale-radius contact in the limb. We demonstrate that Hynobius amjiensis is the first known living salamander species with a stapedial foramen whose absence was believed to unite salamanders and anurans, and hence opens major questions on the evolution of the middle ear in modern amphibians: if some salamanders and caecilians had a stapedial foramen inherited from their common ancestor, when and how many times was the foramen lost independently in modern amphibians, and how did this structural loss impact the phylogenetic evolution of salamander clades? Our findings of hyper-ossified pectoral and pelvic girdles and loss of postminimus in the pes in H. amjiensis demonstrate that functional morphological features in hynobiids are potentially informative in phylogeny and ontogeny of early salamanders.

Environmentally cued hatching (ECH) is widespread in animals and requires regulation of hatching mechanisms. Enzymatic digestion of the egg membrane is a common hatching mechanism in vertebrates and invertebrates. In amphibians and fishes, hatching enzymes (HE) are synthesized and released by hatching gland cells (HGC), whose functional ontogeny determines when hatching can occur. Ontogenetic studies of HGC development or HE expression are limited, based largely on external cell morphology; few markers for HGC or HE are available, and those appear specific for Xenopus. Moreover, mechanisms regulating HE release are unknown in anurans. To investigate variation in the hatching process, we need tools to identify and analyze its components. Agalychnis callidryas (Hylidae) is a well-established model of ECH, showing plastically timed, acute HE release, unlike the gradual release described for some aquatic anurans. We developed a new antibody marker for A. callidryas HE that also labels HGC/HE in glassfrogs (Centrolenidae). As glassfrogs and treefrogs diverged 62 mya, the antibody may be broadly useful in anurans. We used the AcHE antibody to examine the development and distribution of HGC and accumulation of HE, two key elements of hatching mechanisms, in A. callidryas. We found a much larger number (ca. 4200) and broader distribution of HGC than has been documented in any amphibian, with HGC densely but non-contiguously distributed over the front of the head and eyes and scattered along the dorsal midline. HE expression begins before hatching competence and is strong throughout the plastic hatching period, unlike HE gene expression which diminishes after competence. The distribution and expression ontogeny of A. callidryas' HE/HGC appear related to their hatching performance, plasticity, and embryo morphology. The AcHE antibody will enable comparative research to elucidate co-variation in the functional morphology, performance, and ecological context of hatching.

A major goal of evolutionary ecology is to understand the interaction between ecological differences and the functional morphology of organisms. Studies of this type are common among flying birds but less so in penguins. Penguins (Spheniscidae) are the most derived extant underwater flying birds using their wings for swimming and beak when foraging. The Humboldt Penguin (Spheniscus humboldti) and Magellanic Penguin (S. magellanicus) occur along the coast of South America and their morphology was compared in allopatry and sympatry throughout their ranges. Measurements included: mass, tarsus length, four beak/head dimensions, bite force, wing loading, and aspect ratio. A thin-plate spline/relative warp analysis was also used to detect subtle differences in wing shape. Both species generally overlapped in trait morphology, but Magellanic Penguins showed greater trait diversity. Wing morphology was more homogenous between species than beak morphology indicating a similar mode of locomotion but potential differences in prey procurement. Morphological character displacement in sympatry was only evident in beak length. Local adaptation was common in other traits, and Punta Norte (Argentina) was often distinct in having high variation, notably in beak depth, wing loading, and wing shape (relative warp 1). This may be attributed to the fact that penguins here dive deep and forage farther from their colony; they also have a greater colony size that may contribute to greater intraspecific competition for resources. These results support a potentially optimal wing design for aquatic movement, which likely applies to other penguin species. Differences in morphology may also be related to differences between Atlantic and Pacific ecosystems.

Although numerous studies have addressed some aspects of the cranial osteology of Nearctic dipsadid species, only the species within the genera Heterodon and Carphophis have a formal published description of their skull. Similarly, vertebral data on such species are extremely scarce, and most of the available literature is focused on fossils. Such group has a complex phylogenetic history, being recovered as monophyletic or nonmonophyletic depending on the approach. In this paper, we provide detailed and comparative descriptions of the osteology of dipsadid species distributed in the Nearctic region based on 69 specimens of dry material and high-resolution computed tomography (CT) scans. Additionally, we explore the morphological variation of the skull and cervical vertebrae within the context of distinct phylogenetic hypotheses previously proposed. Only two suprageneric groups previously proposed shared exclusive morphological traits: (Carphophis amoenus + Contia tenuis), proposed by three studies, and (Diadophis punctatus (Ca. amoenus + Co. tenuis)), proposed by one study. Large and detailed studies on the skull, mandible, and vertebrae represent an important step toward the understanding of the evolution of species, especially when they also show intraspecific variation.

Dental anomalies are frequent in boars and pigs, and they generally affect the first premolar loci. The prevalence of these dental anomalies was investigated in a large number of populations around the world. These studies mainly focused on the influence of domestication, size, sexual dimorphism or food hardness on these anomalies. However, they rarely considered ontogenetic aspects, while these are crucial for understanding their aetiology during animal growth and how the dental row-jaw complex is affected. Here, we studied the incidence of missing first upper and lower premolars in a French population of captive wild boars to discuss the functional and developmental reasons for missing teeth and to assess the impact of missing teeth on the growth of the dental row-jaw complex. Using the CT-scan data of the cranium and mandible of 24 wild boars investigated six times each during their growth, and presenting a balanced sex ratio, we recorded the number of missing teeth. We then quantified the shape of the upper and lower jaws using 3D geometric morphometrics. We found a similar prevalence of missing first premolar (37.5%) between the upper and the lower jaws, which is higher than the frequencies observed in most continental populations of wild boars. The increasing number of anomalies during ontogeny suggests a relaxed constraint on the dentition associated with a different feeding behaviour in captivity. The absence of first premolars does not appear to be associated with size variation or sexual dimorphism, nor does it affect the place of the dentition within the jaw, the latter being more influenced by the dimorphic shape of the canines and the timing of dental eruption.